Re: [PATCH net] can: isotp: isotp_rcv_cf(): fix so->rx race problem

[Oliver Hartkopp]

On 18.01.22 13:46, Ziyang Xuan (William) wrote:
> > Hi,
> >
> > the referenced syzbot issue has already been fixed in upstream here:
> >
> > https://git.kernel.org/pub/scm/linux/kernel/git/netdev/net.git/commit/?id=5f33a09e769a9da0482f20a6770a342842443776
> >
> > ("can: isotp: convert struct tpcon::{idx,len} to unsigned int")
> >
> > Additionally this fix changes some behaviour that is required by the ISO 16765-2 specification (see below).
> >
> > On 17.01.22 13:01, Ziyang Xuan wrote:
> > > When receive a FF, the current code logic does not consider the real
> > > so->rx.state but set so->rx.state to ISOTP_IDLE directly. That will
> > > make so->rx accessed by multiple receiving processes concurrently.
> >
> > This is intentionally. "multiple receiving processes" are not allowed resp. specified by ISO 15765-2.
>
> Does it can be a network attack?

Yes. You can see it like this. The ISO 15765-2 protocol is an unreliable 
UDP-like datagram protocol and the session layer takes care about 
timeouts and packet lost.

If you want to disturb that protocol you can also send PDUs with 
out-of-sync packet counters which will make the receiver drop the 
communication attempt.

This is 'CAN-style' ... as usually the bus is very reliable. Security 
and reliable communication is done on top of these protocols.

> It receives packets from network, but unexpected packets order make server panic.

Haha, no :-)

Unexpected packets should not make the server panic but only drop the 
communication process.

In the case pointed out by syzbot the unsigned 32 bit length information 
was stored in a signed 32 bit integer which caused a sanity check to fail.

This is now fixed with the patch from Marc.

Regards,
Oliver